Methods and systems for mitigating interference with a nearby satellite

ABSTRACT

In one embodiment, an antenna system is described. The antenna system includes a primary antenna on an aircraft. The primary antenna is mechanically steerable and has an asymmetric antenna beam pattern with a narrow beamwidth axis and a wide beamwidth axis at boresight. The antenna system also includes a secondary antenna on the aircraft, the secondary antenna including an array of antenna elements. The antenna system also includes an antenna selection system to control communication of a signal between the aircraft and a target satellite via the primary antenna and the secondary antenna. The antenna selection system switches communication of the signal from the primary antenna to the secondary antenna when an amount of interference with an adjacent satellite reaches a threshold due to the wide beamwidth axis of the asymmetric antenna beam pattern.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application for patent is a continuation of U.S. patentapplication Ser. No. 16/846,780 by Diamond et al., entitled “Methods andSystems For Mitigating Interference With A Nearby Satellite” filed Apr.13, 2020, which is a continuation of U.S. patent application Ser. No.16/163,808 titled “Methods and Systems for Mitigating Interference witha Nearby Satellite” filed Oct. 18, 2018, which is a continuation of U.S.patent application Ser. No. 15/165,539, titled “Methods and Systems forMitigating Interference with a Nearby Satellite”, filed May 26, 2016,which claims priority to U.S. Patent Application No. 62/171,418, titled“Methods and Systems for Mitigating Interference with a NearbySatellite”, filed Jun. 5, 2015, each of which is assigned to theassignee hereof and expressly incorporated by reference herein for anyand all purposes.

BACKGROUND

The present disclosure relates generally to satellite communications,and more specifically to airborne systems and methods for using suchsystems to avoid excessive interference with one or more non-targetsatellites during communication with a target satellite.

A geostationary satellite is a satellite that is in geostationary Earthorbit (GEO) about 35,800 km above Earth's equator, and has a revolutionaround the Earth synchronized with Earth's rotation. As a result, thegeostationary satellite appears stationary to an observer on the Earth'ssurface.

Geostationary satellites occupy orbital slots separated in longitudealong the geostationary arc above the Earth's equator. Thesegeostationary satellites, which operate using various frequencies andpolarizations, provide a variety of broadcast and communicationservices. Other types of satellites include low Earth orbit (LEO)satellites set between about 160 km and 2,000 km above Earth's surface,and medium Earth orbit (MEO) satellites set in orbit with an altitudegreater than about 2,000 km and less than about 35,800 km above Earth'ssurface.

An Earth-based antenna terminal for communication with a satellitetypically has high antenna gain and a narrow main beam pointed at thesatellite, because of the large distance to the satellite and to avoidinterference with other satellites. In order to satisfy interferencerequirements with the other satellites, a mobile antenna terminal mayonly be permitted to communicate with the target satellite when atcertain geographic locations. In such a case, services provided by thesatellite are unavailable to users of the mobile antenna terminal whileat these locations, even though they are within the coverage area of thesatellite.

SUMMARY

In one embodiment, an antenna system for mounting on an aircraft isdescribed. The antenna system includes a primary antenna on theaircraft. The primary antenna is mechanically steerable and has anasymmetric antenna beam pattern with a narrow beamwidth axis and a widebeamwidth axis at boresight. The antenna system also includes asecondary antenna on the aircraft. The secondary antenna includes anarray of antenna elements. The antenna system also includes an antennaselection system to control communication of a signal between theaircraft and a target satellite via the primary antenna and thesecondary antenna. The antenna selection system switches communicationof the signal from the primary antenna to the secondary antenna when anamount of interference with a non-target satellite reaches a thresholddue to the wide beamwidth axis of the asymmetric antenna beam pattern.

In another embodiment, a method is described that includes communicatinga signal between a target satellite and an aircraft via a primaryantenna on the aircraft. The primary antenna is mechanically steerableand has an asymmetric antenna beam pattern with a narrow beamwidth axisand a wide beamwidth axis at boresight. The method also includesdetermining that an amount of interference with a non-target satellitereaches a threshold due to the wide beamwidth axis of the asymmetricantenna beam pattern. The method also includes, in response to thedetermination, switching communication of the signal from the primaryantenna to a secondary antenna on the aircraft to reduce interferencewith the non-target satellite. The secondary antenna includes an arrayof antenna elements.

In yet another embodiment, an antenna system for mounting on an aircraftfor communication with a target satellite is described. The antennasystem includes a primary antenna comprising a first array of antennaelements and a positioner. The first array of antenna elements has afirst main beam with a horizontal half-power beamwidth along ahorizontal axis of the first array and has a vertical half-powerbeamwidth along a vertical axis of the first array. The verticalhalf-power beamwidth is greater than the horizontal half powerbeamwidth. The positioner is rotatably coupled with the first arrayabout at least a first axis and a second axis to point the first mainbeam at the target satellite. The first main beam has a composite halfpower beamwidth that is less than or equal to a particular value over afirst range of skew angles. The first main beam has a composite halfpower beamwidth that is greater than the particular value over a secondrange of skew angles. The antenna system also includes a secondaryantenna oriented relative to the primary antenna. The secondary antennaincludes a second array of antenna elements having a second main beamand a steering mechanism to point the second main beam at the targetsatellite. The second main beam has a composite half power beamwidththat is less than or equal to the particular value over the second rangeof skew angles. The antenna system also includes an antenna selectionsystem to select between the primary antenna and the secondary antennafor communication of a signal with the target satellite based on theskew angle.

In yet another embodiment, an antenna system for mounting on an aircraftis described. The antenna system includes a primary antenna on theaircraft. The primary antenna has a first acceptable service area forcommunication of a signal between the aircraft and a target satellitewhile satisfying an interference requirement with a non-targetsatellite. The antenna system also includes a secondary antenna on theaircraft. The secondary antenna has a second acceptable service area forcommunication of the signal between the aircraft and the targetsatellite while satisfying the interference requirement with thenon-target satellite. The second acceptable service area is differentthan the first acceptable service area. The antenna system also includesan antenna selection system to control communication of the signalbetween the aircraft and the target satellite via the primary antennaand the secondary antenna. The antenna selection system switchescommunication of the signal between the primary antenna and thesecondary antenna based on a geographic location of the aircraft and thefirst and second acceptable service areas.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example satellite communications system in whichan antenna system as described herein can be used to avoid excessiveinterference with one more satellites.

FIG. 2 is a block diagram illustrating an example antenna system on theaircraft of FIG. 1.

FIG. 3 illustrates a perspective view of an example primary antenna andan example secondary antenna of an example antenna system.

FIG. 4A illustrates a perspective view of the main beam of an exampleasymmetric antenna pattern of an example primary antenna.

FIG. 4B illustrates an example half-power contour of the asymmetricantenna pattern of main beam FIG. 4A.

FIG. 4C illustrates an example contour of the main beam of the secondaryantenna at a particular scan angle to the target satellite, overlayedwith the contour of main beam of FIG. 4B.

FIG. 5A illustrates an example acceptable service area of the primaryantenna.

FIG. 5B illustrates the contour of the main beam of the primary antennafor an example geographic location within the acceptable service area.

FIG. 5C illustrates the contour of the main beam of the primary antennafor an example geographic location outside the acceptable service area.

FIG. 5D illustrates an example acceptable service area of the secondaryantenna.

FIG. 5E illustrates an example composite acceptable service area for theantenna system.

FIG. 6 is an example graph of maximum power spectral density (PSD)curves for the primary antenna and the secondary antenna that satisfyinterference requirements with the non-target satellite.

FIG. 7 is an example plot of the maximum value of the gain of theprimary antenna at 2 degrees from boresight of the main beam versus skewangle.

FIG. 8 illustrates an example process for switching between the primaryantenna and the secondary antenna.

DETAILED DESCRIPTION

An airborne antenna system described herein can provide efficientcommunication with a target satellite over a large geographical area,while also satisfying interference requirements with other satellites.In some embodiments, the airborne antenna system can providenon-interfering communication with a target satellite, over the entireor substantially the entire coverage area (or footprint) of the targetsatellite. In doing so, services such as Internet, telephone and/ortelevision services provided by the target satellite can be delivered toairborne users throughout most or all of the satellite's coverage area,while also satisfying interference requirements with other satellites.

The antenna system can include a primary antenna and a secondary antennaon an aircraft such as an airplane. The antenna system can also includean antenna selection system to control communication of one or moresignals between the aircraft and the target satellite via the primaryantenna and the secondary antenna.

The primary antenna can be mechanically steerable about at least oneaxis to point a main beam of the primary antenna at the targetsatellite. As used herein, a main beam of an antenna that is “pointed”at a satellite has sufficient antenna gain in the direction of thetarget satellite to permit communication of one or more signals. Thecommunication can be bidirectional (i.e., the antenna transmits a signalto the satellite and also receives a signal from the satellite) orunidirectional (i.e., the antenna either transmits a signal to thesatellite or receives a signal from the satellite, but not both). Thedirection of the target satellite may be boresight of the antenna. Asused herein, “boresight” of an antenna refers to the direction ofmaximum gain of the antenna. Alternatively, the gain in the direction ofthe target satellite may be less than the maximum gain of the antenna.In other words, the direction of the satellite may not be in the exactcenter of the main beam of the antenna. This may for example be due tomotion induced pointing accuracy limitations of the antenna.

In embodiments described herein, the primary antenna has a non-circularantenna aperture that results in an asymmetric antenna beam pattern atboresight. The non-circular shape of the antenna aperture can be due tothe combination of electrical performance requirements and sizeconstraints. Specifically, the non-circular antenna aperture of theprimary antenna is designed to have a large enough effective area toprovide sufficient antenna gain to satisfy link requirements between theaircraft and the target satellite under various operational conditions,while also having a swept volume small enough that it can be housedunder an aerodynamic radome on the aircraft. The primary antenna canvary from embodiment to embodiment. In one embodiment, the primaryantenna is an array of antenna elements arranged in a rectangular panel.

The asymmetric antenna beam pattern of the primary antenna has a narrowbeamwidth axis and a wide beamwidth axis at boresight. As described inmore detail below, when the antenna system is at certain geographiclocations, the wide beamwidth axis can give rise to excessiveinterference with one or more other (non-target) satellites, if theprimary antenna were used to communicate with the target satellite.

The antenna system described herein can avoid the excessive interferencethat could result due to the wide beamwidth axis of the primary antenna,thereby allowing non-interfering communication with the target satelliteover a large geographic area. As described in more detail below, theantenna system includes a secondary antenna, which can be locatedunderneath the same radome as the primary antenna, and an antennaselection system. The secondary antenna can be a different type ofantenna than the primary antenna, and/or have a different beam steeringmechanism than the primary antenna.

The antenna selection system controls whether the primary antenna or thesecondary antenna is used to communicate each of the one or more signalscommunicated between the aircraft and the target satellite. Using thetechniques described herein, the antenna selection system can determinewhen the amount of interference with one or more non-target satellitesusing the primary antenna, due to the wide beamwidth axis, reaches athreshold. In response to the determination, the antenna selectionsystem can switch to communicating with the target satellite using thesecondary antenna. In doing so, the antenna system described herein canprovide communication with the target satellite at locations where useof the primary antenna is precluded due to interference requirements. Asa result, the service area over which services provided by the targetsatellite can be delivered to airborne users can be larger as comparedto only using the primary antenna.

FIG. 1 illustrates an example satellite communications system 100 inwhich an antenna system 150 as described herein can be used to avoidexcessive interference with one more satellites. Many otherconfigurations are possible having more or fewer components than thesatellite communication system 100 of FIG. 1.

As can be seen in FIG. 1, the antenna system 150 is mounted on aircraft102. In the illustrated embodiment, the aircraft 102 is an airplane.Alternatively, the antenna system 150 can be mounted to other types ofaircraft, such as a helicopter, drone, etc.

As described in more detail below, the antenna system 150 facilitatescommunication between the aircraft 102 and satellite 110 (hereinafterreferred to as the “target satellite 110”), while also satisfyinginterference requirements with one or more other (non-target)satellites. The antenna system 150 includes an antenna selection system(not shown) to control communication of one or more signals with thetarget satellite 110 via a primary antenna 152 and a secondary antenna154, using the techniques described herein. In the illustratedembodiment, the primary antenna 152 and the secondary antenna 154 arelocated under the same radome 156. Alternatively, the primary antenna152 and the secondary antenna 154 can be located under separate radomeson the aircraft.

In some embodiments in which the primary antenna 152 and the secondaryantenna 154 are located under the same radome 156, the shape of theradome 156 may designed to house the primary antenna 152 and satisfyaerodynamic requirements, and the secondary antenna 154 may be selectedor designed to fit within remaining room under the radome 156.

The antenna system 150 can also include memory for storage of data andapplications, a processor for accessing data and executing applications,and components that facilitate communication over the satellitecommunication system 100. Although only one aircraft 102 is illustratedin FIG. 1 to avoid over complication of the drawing, the satellitecommunications system 100 can include many more aircraft 102 havingrespective antenna systems 150 mounted thereon.

In the illustrated embodiment, the target satellite 110 providesbidirectional communication between the aircraft 102 and a gatewayterminal 130. The gateway terminal 130 is sometimes referred to as a hubor ground station. The gateway terminal 130 includes an antenna totransmit a forward uplink signal 140 to the target satellite 110 andreceive a return downlink signal 142 from the target satellite 110. Thegateway terminal can also schedule traffic to the antenna system 150.Alternatively, the scheduling can be performed in other parts of thesatellite communications system 100 (e.g. a core node, satellite accessnode, or other components, not shown). Signals 140, 142 communicatedbetween the gateway terminal 130 and target satellite 110 can use thesame, overlapping, or different frequencies as signals 112, 114communicated between the target satellite 110 and the antenna system150.

Network 135 is interfaced with the gateway terminal 130. The network 135can be any type of network and can include for example, the Internet, anIP network, an intranet, a wide area network (WAN), a local area network(LAN), a virtual private network (VPN), a virtual LAN (VLAN), a fiberoptic network, a cable network, a public switched telephone network(PSTN), a public switched data network (PSDN), a public land mobilenetwork, and/or any other type of network supporting communicationbetween devices as described herein. The network 135 can include bothwired and wireless connections as well as optical links. The network 135can include both wired and wireless connections as well as opticallinks. The network 135 can connect multiple gateway terminals 130 thatcan be in communication with target satellite 110 and/or with othersatellites.

The gateway terminal 130 can be provided as an interface between thenetwork 135 and the target satellite 110. The gateway terminal 130 canbe configured to receive data and information directed to the antennasystem 150 from a source accessible via the network 135. The gatewayterminal 130 can format the data and information and transmit forwarduplink signal 140 to the target satellite 110 for delivery to theantenna system 150. Similarly, the gateway terminal 130 can beconfigured to receive return downlink signal 142 from the targetsatellite 110 (e.g. containing data and information originating from theantenna system 150) that is directed to a destination accessible via thenetwork 135. The gateway terminal 130 can also format the receivedreturn downlink signal 142 for transmission on the network 135.

The target satellite 110 can receive the forward uplink signal 140 fromthe gateway terminal 130 and transmit corresponding forward downlinksignal 114 to the antenna system 150. Similarly, the target satellite110 can receive return uplink signal 116 from the antenna system 150 andtransmit corresponding return downlink signal 142 to the gatewayterminal 130. The target satellite 110 can operate in a multiple spotbeam mode, transmitting and receiving a number of narrow beams directedto different regions on Earth. Alternatively, the target satellite 110can operate in wide area coverage beam mode, transmitting one or morewide area coverage beams.

The target satellite 110 can be configured as a “bent pipe” satellitethat performs frequency and polarization conversion of the receivedsignals before retransmission of the signals to their destination. Asanother example, the target satellite 110 can be configured as aregenerative satellite that demodulates and remodulates the receivedsignals before retransmission.

As shown in FIG. 1, the satellite communications system 100 alsoincludes another satellite 120 (hereinafter referred to as “non-targetsatellite 120”). Communication of one or more signals between thenon-target satellite 120 and the antenna system 150 is undesired orunintended. Although only one non-target satellite 120 is illustrated inFIG. 1 to avoid over complication of the drawing, the satellitecommunications system 100 can include many more non-target satellites120 and the techniques described herein can be used to avoid excessiveinterference with each of the non-target satellites 120.

The non-target satellite 120 can, for example, be configured as a bentpipe or regenerative satellite. The non-target satellite 120 cancommunicate one or more signals with one or more ground stations (notshown) and/or other terminals (not shown).

As mentioned above, the antenna system 150 includes an antenna selectionsystem to control communication with the target satellite 110 via theprimary antenna 152 and the secondary antenna 156, while also avoidingexcessive interference with the non-target satellite 120. The antennasystem 150 is described in more detail below with respect to FIGS. 2-3and others.

As used herein, interference “with” the non-target satellite 120 canrefer to uplink interference and/or downlink interference. Uplinkinterference is interference to the non-target satellite 120 caused by aportion of the return uplink signal 116 transmitted by the antennasystem 150 that is received by the non-target satellite 120. Downlinkinterference is interference to the antenna system 150 caused by aportion of a signal transmitted by the non-target satellite 120 that isreceived by the antenna system 150.

In the illustrated embodiment, the target satellite 110 and thenon-target satellite 120 are each geostationary satellites. Thegeostationary orbit slots, and thus the angular separation along thegeostationary arc between the target satellite 110 and the non-targetsatellite 120, can vary from embodiment to embodiment. In someembodiments the angular separation along the geostationary arc is atleast two degrees. In alternative embodiments, one or both of the targetsatellite 110 and the non-target satellite 120 can be anon-geostationary satellite, such as a LEO or MEO satellite. Thenon-target satellite 120 can for example be adjacent to the targetsatellite 110. As used herein, the target satellite 110 and thenon-target satellite 120 are “adjacent” if the effective angularseparation between them as viewed at antenna system 150 is less than orequal to 10 degrees.

FIG. 2 is a block diagram illustrating an example antenna system 150 onthe aircraft 102 of FIG. 1. The antenna system 150 can include primaryantenna 152, secondary antenna 154, antenna selection system 200,transceiver 210, modem 230, network access unit (NAU) 240, and wirelessaccess point (WAP) 250. Many other configurations are possible havingmore or fewer components than the antenna system 150 shown in FIG. 2.Moreover, the functionalities described herein can be distributed amongthe components in a different manner than described herein.

In the illustrated embodiment, the primary antenna 152 and the secondaryantenna 154 are each housed under the same radome 156 disposed on thetop of the fuselage or other location (e.g., on the tail, etc.) of theaircraft 102. Alternatively, the primary antenna 152 and the secondaryantenna 154 can be housed under separate radomes which can be located indifferent locations on the aircraft 102.

The antenna system 150 can provide for transmission of the forwarddownlink signal 114 and reception of the return uplink signal 116 tosupport two-way data communications between data devices 260 within theaircraft 102 and the network 135 via target satellite 110 and gatewayterminal 130. The data devices 260 can include mobile devices (e.g.,smartphones, laptops, tablets, netbooks, and the like) such as personalelectronic devices (PEDs) brought onto the aircraft 102 by passengers.As further examples, the data devices 260 can include passenger seatback systems or other devices on the aircraft 102. The data devices 260can communicate with the network access unit 240 via a communicationlink that can be wired and/or wireless. The communication link can be,for example, part of a local area network such as a wireless local areanetwork (WLAN) supported by WAP 250. One or more WAPs can be distributedabout the aircraft 102, and can, in conjunction with network access unit240, provide traffic switching or routing functionality; for example, aspart of a WLAN extended service set (ESS), etc. The network access unit240 can also allow passengers to access one or more servers (not shown)local to the aircraft 102, such as a server that provides in-flightentertainment.

In operation, the network access unit 240 can provide uplink datareceived from the data devices 260 to the modem 230 to generatemodulated uplink data (e.g. a transmit IF signal) for delivery to thetransceiver 210. The transceiver 210 can upconvert and then amplify themodulated uplink data to generate the return uplink signal 116 (FIG. 1)for transmission to the target satellite 110 (FIG. 1) via the primaryantenna 152 or the secondary antenna 154. Similarly, the transceiver 210can receive the forward downlink signal 114 (FIG. 1) from the targetsatellite 110 (FIG. 1) via the primary antenna 152 or the secondaryantenna 154. The transceiver 210 can amplify and then downconvert theforward downlink signal 114 to generate modulated downlink data (e.g., areceive IF signal) for demodulation by the modem 230. The demodulateddownlink data from the modem 230 can then be provided to the networkaccess unit 240 for routing to the data devices 260. The modem 230 canbe integrated with the network access unit 240, or can be a separatecomponent, in some examples.

In the illustrated embodiment, the transceiver 210 is located outsidethe fuselage of the aircraft 102 and under the radome 156.Alternatively, the transceiver 210 can be located in a differentlocation, such as within the aircraft interior. In the illustratedembodiment, the transceiver 210 is shared between the primary antenna152 and the secondary antenna 154. Alternatively, the antenna system 150may include a first transceiver coupled to the primary antenna 152, anda second transceiver coupled to the secondary antenna 154. In such acase, the modem 230 may be shared by the first transceiver and thesecond transceiver, or may use separate modems.

As described in more detail below, the antenna selection system 200 cancontrol whether the primary antenna 152 or the secondary antenna 154 isused to receive the forward downlink signal 114 from the targetsatellite 110, and also whether the primary antenna 152 or the secondaryantenna 154 is used to transmit the return uplink signal 116 to thetarget satellite 110. The functions of the antenna selection system 200can be implemented in hardware, instructions embodied in a memory andformatted to be executed by one or more general or application-specificprocessors, firmware, or any combination thereof. In the illustratedembodiment, the antenna selection system 200 is shown as a separatedevice. Alternatively, some or all of the components or features of theantenna selection system 200 can be implemented within one or more othercomponents of the antenna system 150. In the illustrated embodiment, theantenna selection system 200 is located under the radome 156.Alternatively, some or all of the antenna selection system 200 can belocated in a different location, such as within the aircraft interior.As another example, some or all of the antenna selection system 200 maybe located in other parts of the satellite communications system 100,such as the gate terminal 130, a core node, satellite access node, orother components not shown.

The primary antenna 152 can include an array of antenna elements thatare operable over the frequency ranges of both the forward downlinksignal 114 and the return uplink signal 116. In such a case, the sameantenna elements of the array can transmit the return uplink signal 116and receive forward downlink signal 114. Alternatively, the primaryantenna 152 can include a first group of one or more antenna elements totransmit the return uplink signal 116, and a second group of one or moreantenna elements to receive forward downlink signal 114.

The primary antenna 152 can include a positioner rotatably coupled tothe array of the primary antenna 152 to mechanically steerable the arrayabout at least one axis to point the main beam of the array of theprimary antenna 210 at the target satellite 110 as the aircraft 102moves. In some embodiment, the primary antenna 152 is fully mechanicallysteered using an elevation-over-azimuth (EL/AZ), two-axis positioner.Alternatively, the positioner may include other mechanisms for providingadjustment in azimuth and elevation. For example, in some alternativeembodiments, the primary antenna 152 can include a combination ofmechanical and electrical scanning mechanisms. As another example, theprimary antenna 152 includes a fully mechanically steered usingthree-axis positioner to provide adjustment in azimuth, elevation andskew. The primary antenna 152 can also include an antenna control unitto provide control signals to the positioner.

The primary antenna 152 has a non-circular antenna aperture that resultsin an asymmetric antenna beam pattern of the main beam at boresight. Thenon-circular shape of the antenna aperture can be due to the combinationof electrical performance requirements and size constraints.Specifically, the non-circular antenna aperture of the primary antenna152 can be designed to have a large enough effective area to providesufficient antenna gain to satisfy link requirements between theaircraft 102 and the target satellite 110 under various operationalconditions, while also having a swept volume small enough that it can behoused under an aerodynamic radome 156 on the aircraft 102.

The primary antenna 152 can be any type of antenna that fits under anaerodynamic radome and provides an asymmetric antenna beam pattern, andcan vary from embodiment to embodiment. In some embodiments, the primaryantenna 152 is an array of waveguide antenna elements arranged in arectangular panel. Each of the one or more antenna elements can includea waveguide-type feed structure including a horn antenna. Alternatively,other types of structures and antenna elements can be used for theprimary antenna 210. For example, in another embodiment, the primaryantenna 210 can include one or more feeds illuminating a reflectorhaving an asymmetric reflector surface. As another example, the primaryantenna 152 can include multiple, separately moveable panels thattogether provides an asymmetric antenna aperture.

The asymmetric antenna beam pattern of the primary antenna 152 has awide beamwidth axis and a narrow beamwidth axis. As described in moredetail below, when the antenna system 150 (and thus the aircraft 102) isat certain geographic locations, the wide beamwidth axis can give riseto excessive interference with the non-target satellite 120, if theprimary antenna 152 were used to communicate with the target satellite110.

When using the primary antenna 152 to communicate with the targetsatellite 110, the antenna selection system 200 can switch tocommunicating with the target satellite 110 using the secondary antenna154 when the amount of interference with the non-target satellite 120,due to the wide beamwidth axis, reaches a threshold. In doing so, theantenna system 150 can provide communication with target satellite 110at geographic locations where use of the primary antenna 152 isprecluded due to interference requirements. As a result, the techniquesdescribed herein can ensure that the interference generated is withinacceptable limits to other satellite system operators, while at the sametime satisfying link requirements between the aircraft 102 and thetarget satellite 110.

The secondary antenna 154 can include an array of antenna elements and asteering mechanism for pointing a main beam of the array at the targetsatellite 110 as the aircraft 102 moves. The secondary antenna 154 canbe a different type of antenna than the primary antenna 152, and/or havea different beam steering mechanism than the primary antenna 152. Asdescribed in more detail below, the secondary antenna 152 is arrangedrelative to the primary antenna, and has different composite beamwidthcharacteristics versus skew angle than the primary antenna 152 atvarious geographic locations, such that the secondary antenna 154 canprovide an acceptable service area for communication with targetsatellite 110 that is different than the acceptable service areaprovided by the primary antenna 152.

Thus, at a given geographic location that is within the acceptableservice area of the secondary antenna 154 and also outside theacceptable service area of the primary antenna 152, the secondaryantenna 154 can satisfy interference requirements with the non-targetsatellite 110. In other words, switching to the secondary antenna 154can reduce interference with the non-target satellite 120 as compared tothe primary antenna 152, while still permitting communication betweenthe aircraft 102 and the target satellite 110. In doing so, thesecondary antenna 152 can provide for communication with the targetsatellite 110 at geographic locations where use of the primary antenna152 is precluded due to interference requirements.

At some or all of geographic locations for the aircraft 102, the primaryantenna 152 may be designed to provide better performancecharacteristics than the secondary antenna 154 for communicating atleast one of the return uplink signal 116 and the forward downlinksignal 114 with the target satellite 110. For example, the primaryantenna 152 can have one or more of higher gain, lower sidelobes,cross-polarization, etc.

As used herein, the interference “with” non-target satellite 120 can beuplink interference and/or downlink interference. Uplink interference isinterference to the non-target satellite 120 caused by electromagneticenergy from a portion of the return uplink signal 116 that is receivedby the non-target satellite 120. Downlink interference is interferenceto the antenna system 150 caused by radiated electromagnetic energy fromthe non-target satellite 120 that is received by the antenna system 150.The downlink interference can increase the equivalent noise temperatureat a receiver of the antenna system 150, which in turn reduces thesignal-to-noise ratio of the forward downlink signal 114 received by theantenna system 150.

The antenna selection system 200 can switch between the primary antenna152 and the secondary antenna 154 based one or more thresholds for theamount of interference with the non-target satellite 120. The one ormore thresholds can be based on uplink interference and/or downlinkinterference and can vary from embodiment to embodiment.

In some embodiments, the same threshold can be used for switching fromthe primary antenna 152 to the secondary antenna 154, and for switchingfrom the secondary antenna 152 to the primary antenna 152. In otherwords, the antenna selection system 200 can switch from the primaryantenna 152 to the secondary antenna 154 when the amount of interferencereaches the threshold, and switch back to the primary antenna 152 whenthe amount of interference using the primary antenna 152 will be belowthe threshold. In some other embodiments, the threshold for switchingfrom the primary antenna 152 to the secondary antenna 154 can bedifferent than the threshold for switching from the secondary antenna154 to the primary antenna 152. In such a case, the antenna selectionsystem 200 can avoid rapidly switching between the antennas 152, 154when the aircraft 102 is near the boundary of the acceptable servicearea of the primary antenna 152.

In some embodiments, the value of the threshold for switchingtransmission of the return uplink signal 116 from the primary antenna152 to the secondary antenna 154 can for example be based on regulatoryrequirements imposed by regulatory agencies (e.g. FCC, ITU, etc.) on themaximum power spectral density (or other metric) that can be radiated tothe non-target satellite 120, or coordination agreements with theoperator of the non-target satellite 120. Additionally, the thresholdfor switching transmission of the return uplink signal 116 from theprimary antenna 152 to the secondary antenna 154 can account for one ormore of motion induced pointing accuracy limitations of the primaryantenna 152, etc.

The antenna selection system 200 can determine when to switch based on acomparison(s) of the threshold(s) to the amount of interference with thenon-target satellite 120 at the current geographic location and attitudeof the aircraft 102. The current geographic location may for example beprovided via a global positioning system (GPS) or other equipment on theaircraft 102. The attitude (including yaw, roll and pitch) of theaircraft 102 may for example be provided via an internal reference unit(IRU) on the aircraft 102.

The amount of interference at a given geographic location can bedetermined using various techniques, and can be characterized orrepresented in different ways. For example, in some embodiments theamount of interference is represented in terms of power spectral density(PSD).

The amount of uplink interference can for example be determined based onone or more of the known antenna pattern characteristics of the primaryantenna 152 and the secondary antenna 154, the transmission parameters(e.g. transmit power, frequency range, etc.) of the return uplink signal116, the geographic location of the aircraft 102, the attitude of theaircraft 102, the locations of the target satellite 110 and non-targetsatellite 120, the operating frequency, system gain-to noise temperature(G/T) and/or polarization of operation of the non-target satellite 120,etc. Alternatively, other and/or additional information can be used tocalculate the amount of interference. The amount of downlinkinterference can be calculated in a similar manner based on theparameters of a signal from the non-target satellite 120 that isreceived by the antenna system 150.

In some embodiments, the comparison of the threshold(s) to the amount ofinterference at the various geographic locations has been previouslycalculated for each of the primary antenna 152 and the secondary antenna154. In such a case, the antenna selection system 200 can store alook-up table indicating which of the primary antenna 152 and secondaryantenna 154 to use based on the current geographic location and attitudeof the aircraft 102.

The manner in which the antenna selection system 200 controls theswitching between the primary antenna 152 and the secondary antenna 154can vary from embodiment to embodiment. In some embodiments, the antennaselection system 200 provides control signals to the transceiver 210 (ortransceivers) to enable/disable operation of electronics associated withthe primary antenna 152 and the secondary antenna 154. In otherembodiments, the antenna selection system 200 controls switches thatroute the signals between the modem 230 and the antennas 152, 154through the transceiver 210. Alternatively, other techniques can beused.

In some embodiments, the antenna selection system 200 switches both thetransmission of return uplink signal 116 and the reception of forwarddownlink signal 114 when switching between the primary antenna 152 andthe secondary antenna 154. In such a case, the same antenna (eitherprimary antenna 152 or the secondary antenna 154) is used fortransmitting the return uplink signal 116 and for receiving the forwarddownlink signal 114 at a particular time during operation.

In some other embodiments, the antenna selection system 200 switchesonly one of the transmission of return uplink signal 116 and thereception of forward downlink signal 114 when switching between theprimary antenna 152 and the secondary antenna 154. For example, inembodiments in which the switching is done to avoid excessive uplinkinterference with the non-target satellite 120, the primary antenna 152can be used to receive forward downlink signal 114 regardless of whetherthe return uplink signal 116 is transmitted via the primary antenna 152or the secondary antenna 154. In doing so, overall system performancecan be improved in embodiments in which downlink interference is notexcessive and the primary antenna 152 can provide better performancecharacteristics (e.g. higher gain, etc.) than the secondary antenna 154for reception of the forward downlink signal 114. Using the secondaryantenna 154 only for transmission of the return uplink signal 116 maysimplify the secondary antenna 154 and the associated electronics. Forexample, the secondary antenna 154 may be operable over the frequencyrange of the return uplink signal 116, but not the frequency range ofthe forward downlink signal 114. In embodiments in which the primaryantenna 152 is coupled to a dedicated transceiver, the secondary antenna154 can be coupled to a transmitter rather than another transceiver. Asanother example, the primary antenna 152 may be coupled to a receiver,and a shared transmitter may be selectively switched between the primaryantenna 152 and the secondary antenna 154.

In addition to switching between the primary antenna 152 and thesecondary antenna 154, the antenna selection system 200 can also changethe transmission parameters of the return uplink signal 116 to avoidexcessive interference when needed. For example, the antenna selectionsystem 200 can change one or more of transmitted power level of thereturn uplink signal 116, spreading the return uplink signal 116 over alarger bandwidth, or any other technique for reducing the power spectraldensity in the direction of the non-target satellite 120.

In some embodiments, the primary antenna 152 and the secondary antenna154 each remain pointed at the target satellite 110 regardless of whichantenna 152, 154 is currently being used. In other words, the antennasystem 150 maintains pointing of the primary antenna 152 and thesecondary antenna 154 at the target satellite 110 following switching ofthe communication with the target satellite 110. In such a case, thehandover time between the primary antenna 152 and the secondary antenna154 can be minimized.

In some embodiments, the antenna system 150 maintains the return linkoperating point (e.g., energy per symbol to noise power spectral densityE_(s)/N₀) regardless of whether the primary antenna 152 and thesecondary antenna 154 is used to transmit the return uplink signal 116.For example, in embodiments in which the gain of the primary antenna 152is greater than the gain and the secondary antenna 154, the antennasystem 150 may increase the transmit power of the return uplink signal116 upon switching from the primary antenna 152 to the secondary antenna154. The antenna system 150 may then reduce the transmit power uponswitching back to the primary antenna 152. In some alternativeembodiments, the antenna system 105 can have different return linkoperating points for the primary antenna 152 and the secondary antenna154. The different operating points can be due to differences in thegains of the primary antenna 152 and the secondary antenna 154, and/ordifferent transmit powers of the return uplink signal 116 when using theprimary antenna 152 and the secondary antenna 154.

FIG. 3 illustrates a perspective view of an example primary antenna 152and an example secondary antenna 154 of an example antenna system 150.

The primary antenna 152 can include a positioner 300 and an array 310 ofantenna elements. The array 310 of antenna elements has a non-circularaperture that includes a major axis 312 (referred to hereinafter as“horizontal axis 312”), which is the longest line through the center ofarray 310 of antenna elements. The array 310 of antenna elements thatalso includes a minor axis (referred to hereinafter as “vertical axis314”), which is the shortest line through the center of the array 310 ofantenna elements. The non-circular aperture of the array 310 of antennaelements defines an antenna beam having an asymmetric antenna beampattern at boresight.

In the illustrated embodiment, the array 310 of antenna elements is adirect radiating two-dimensional array which results in boresight beingnormal to a plane containing the antenna elements of the array 310. As aresult, in the illustrated embodiment the asymmetric antenna beampattern has a narrow beamwidth axis aligned with the horizontal axis 312and a wide beamwidth axis aligned with the vertical axis 314.Alternatively, the array 310 of antenna elements can be arranged and/orfed in a different manner such that boresight is not normal to the planecontaining the antenna elements of the array 310.

The positioner 300 is responsive to commands from an antenna controlunit (not shown) of the antenna system 150 to mechanically steer theprimary antenna 152 to point the main beam of the array 310 in thedirection of the target satellite 110. In the illustrated embodiment thepositioner 300 is an elevation-over-azimuth (EL/AZ) two-axis positionerthat provides full two-axis mechanical steering. The positioner 300includes a mechanical azimuth adjustment mechanism to move the primaryantenna 152 in azimuth 320, and a mechanical elevation adjustmentmechanism to move the primary antenna 152 in elevation 320. Each of themechanical adjustment mechanisms can for example include a motor withgears and other elements to provide for movement of the primary antenna152 around a corresponding axis. In some alternative embodiments, thesteering mechanism for the primary antenna 152 may include a combinationof mechanical and electrical steering of the main beam.

The secondary antenna 154 can include an array 350 of antenna elementshaving a main beam. The secondary antenna 154 includes a steeringmechanism to point the main beam of the array 350 at the targetsatellite 110. The type of antenna elements, orientation of the antennaelements, and the steering mechanism of the secondary antenna 154 canvary from embodiment to embodiment. In some embodiments, the array 350includes antenna elements that are operable over the frequency ranges ofboth the forward downlink signal 114 and the return uplink signal 116.In such a case, the same antenna elements of the array 350 can transmitthe return uplink signal 116 and receive the forward downlink signal114. In some alternative embodiments, the array 350 includes a firstgroup of one or more antenna elements to transmit the return uplinksignal 116, and a second group of one or more antenna elements toreceive the forward downlink signal 114. In embodiments in which thesecondary antenna 154 is only used for transmission of the return uplinksignal 116, the antenna of the array 350 may be operable over thefrequency range of the return uplink signal 116, but not the frequencyrange of the forward downlink signal 114.

In the illustrated embodiment, the antenna elements of the array 350 arearranged in a circular two-dimensional array arranged in a plane 352.Alternatively, the antenna elements of the array 350 may be arranged ina different fashion. For example, the array 350 may have a non-circularantenna aperture that results in an asymmetric antenna beam pattern atboresight. In such a case, the asymmetric antenna beam pattern of thesecondary antenna 154 has a narrow beamwidth axis and a wide beamwidthaxis at boresight. In some embodiments, the steering mechanism of thesecondary antenna 154 includes a mechanical azimuth adjustment mechanismresponsive to commands (e.g., from an antenna control unit, the antennaselection system, etc.) to rotate the secondary antenna 154 in azimuth,and an azimuth/elevation adjustment mechanism to steer the main beam ofthe secondary antenna 154 in the direction of the target satellite. Asthe aircraft 102 moves, the mechanical azimuth adjustment mechanism canbe used to maintain alignment of the narrow beamwidth axis with a linedefined by the target satellite 110 and the non-target satellite 120. Byaligning the narrow beamwidth axis with that line, the amount ofinterference with the non-target satellite 120 can be minimized whilethe secondary antenna 154 is being used.

In the illustrated embodiment, the array 350 is a non-movable, fullyelectronic scanned phased array antenna. The array 350 can include feednetworks and phase controlling devices to properly phase signalscommunicated with some or all the antenna elements of the array 350 toscan the beam in azimuth and elevation from the normal to the plane 352.

Alternatively, the secondary antenna 154 can include a differentsteering mechanism, which can vary based on the antenna type of thesecondary antenna 154. For example, in some alternative embodiments, thesecondary antenna 154 can be an electro-mechanically steered array thatincludes one mechanical scan axis and one electrical scan axis, such asa variably inclined continuous transverse stub (VICTS) antenna. Asanother example, the secondary antenna 154 can be an offset fed,parabolic cylinder reflector antenna, such as an antenna of the type ofDBS-2130 antenna available from L-3 Communications. As yet anotherexample, the secondary antenna 154 can be an EXPLORER 9092H or 9092Mantenna available from Cobham, plc.

The combination of the primary antenna 152 and the secondary antenna 154can vary from embodiment to embodiment. In some embodiments in which thetarget satellite 110 operates at Ka-band, the primary antenna 152 isAero Mobile Terminal Model 2540 available from ViaSat Inc., and thesecondary antenna 154 is a ThinAir Falcon-Ka2517 VICTS antenna availablefrom ThinKom. In embodiments in which the secondary antenna 154 is onlyused for transmission of the return uplink signal 116, the secondaryantenna 154 may only include the transmit antenna aperture of theThinAir Falcon-Ka2517.

FIG. 4A illustrates a perspective view of the main beam 422 of anexample asymmetric antenna pattern of an example primary antenna 152.The main beam 422 has a 3-dB (half power) contour with an ellipticalshape about boresight 430. The positioner 300 (FIG. 3) can move theprimary antenna 152 to point the boresight 430 of the main beam 422 isthe direction of the target satellite 110. The direction can bedescribed in terms of azimuth 424 and elevation 434. Azimuth 424 refersto the angle between boresight 430 and reference 402, and elevation 434refers to the angle between boresight 430 and horizon 401.

FIG. 4B illustrates an example half-power contour of the asymmetricantenna pattern of main beam 422 FIG. 4A. The main beam 422 has a firsthalf-power beamwidth (hereinafter referred to as “horizontal half-powerbeamwidth”) along the narrow beamwidth axis 440 that corresponds thehorizontal axis 312 of the primary antenna 152, and a second half-powerbeamwidth (hereinafter referred to as “vertical half-power beamwidth)along the wide beamwidth axis 450 corresponding to the vertical axis 314of the primary antenna 152. The horizontal half-power beamwidth and thevertical half-power beamwidth can vary from embodiment to embodiments.In some embodiments, the vertical half-power beamwidth is at least threetimes greater than the horizontal half-power beamwidth, such as being atleast four times greater. For example, in some embodiments the verticalhalf-power beamwidth can be less than three degrees, and the horizontalhalf-power beamwidth can be less than one degree. Alternatively, thevertical half-power beamwidth and the horizontal half-power beamwidthmay be different than the examples above.

As shown in FIG. 4B, the main beam 422 has a skew angle 460. As usedherein, “skew angle” refers to the angle between the narrow beamwidthaxis of the main beam of an antenna (e.g. narrow beamwidth axis 440 ofthe main beam 422), and a line defined by the target satellite 110 andthe non-target satellite 120. The half-power beamwidth of the main beam422 along the line defined by the target satellite 110 and non-targetsatellite 120 is referred to herein as a “composite half-powerbeamwidth” 470. The composite half-power beamwidth 470 is a mixture ofthe half-power beamwidths along the narrow beamwidth axis and widebeamwidth axis respectively, and depends on the skew angle 460. Forexample, in embodiments in which the target satellite 110 and thenon-target satellite 120 are geostationary satellites along thegeostationary arc, the skew angle 460 is the angle between the narrowbeamwidth axis 440 and the geostationary arc, and the compositehalf-power beamwidth 470 is the beamwidth along the geostationary arc.

The skew angle 460, and thus the composite half-power beamwidth 470,varies depending upon the geographic location of the aircraft 102 thatincludes the antenna system 150. For example, if the antenna system 150is located at the same longitude as the target satellite 110, the skewangle 460 is zero degrees and the composite half-power beamwidth 470 isthe horizontal half-power beamwidth along the narrow beamwidth axis 440.In such a case, the composite half-power beamwidth 470 can be narrowenough to satisfy interference requirements with the non-targetsatellite 120. However, if the antenna system is located at a differentlongitude than the target satellite 110, the skew angle 460 is non-zeroand the composite half-power beamwidth 470 is a mixture of the verticalhalf-power beamwidth and the horizontal half-power beamwidth. As aresult, at certain geographic locations, the composite half-powerbeamwidth 470 can be wide enough to cause excessive interference withthe non-target satellite 120, if the primary antenna 152 were used tocommunicate with target satellite 110. In other words, due to thevertical half-power beamwidth along the wide beamwidth axis 450, atcertain geographic locations within the service area of the targetsatellite 110, the interference level could exceed the threshold amountof interference with the non-target satellite 120 if the primary antenna152 were used.

FIG. 4C illustrates an example contour of the main beam 480 of thesecondary antenna 154 at a particular scan angle to the target satellite110, overlayed with the contour of main beam 422 of FIG. 4B. Inembodiments in which the secondary antenna 154 is electronically scannedin at least one axis, the contour of the main beam 480 can vary withpointing direction (scan angle) to the target satellite 110. In otherwords, at least one of the vertical half-power beamwidth and thehorizontal half-power beamwidth of the main beam 480 of the secondaryantenna 154 can vary based on the geographic location of the aircraft102. In embodiments in which the primary antenna 152 is fullymechanically steered, the main beam 422 does not vary with pointingdirection.

The vertical half-power beamwidth and the horizontal half-powerbeamwidth of the main beam 480 of the secondary antenna 154 can varyfrom embodiment to embodiment. In some embodiments, the verticalhalf-power beamwidth is less than three times than the horizontalhalf-power beamwidth.

Line 490 represents the maximum acceptable skew angle for the main beam422 of the primary antenna 152 that satisfies interference requirementswith the non-target satellite 120. That is, for a range 492 of skewangles, the composite half-power beamwidth of the main beam 422 is lessthan or equal to a particular value, such that the amount ofinterference with the non-target satellite 120 when using the primaryantenna 152 is at or below the threshold. Accordingly, for a range 494of skew angles, the composite half-power beamwidth of the main beam 422is greater than the particular value, such that the amount ofinterference with the non-target satellite 120 would exceed thethreshold if the primary antenna 152 were used.

As can be seen in FIG. 4B, for the range 494 of skew angles, thecomposite half-power beamwidth of the main beam 480 of the secondaryantenna 154 is less than the particular value of the compositehalf-power beamwidth of the main beam 422 along the line 490. Thus, fora group of geographic locations corresponding to the range 494 of skewangles at which the amount of interference with the non-target satellite120 using the primary antenna 152 exceeds the threshold, theinterference level when using secondary antenna 154 can be less than orequal to the threshold, such that the secondary antenna 154 can be usedto communicate with the target satellite 110. The antenna selectionsystem 200 can thus switch from the primary antenna 152 to the secondaryantenna 154 when the skew angle reaches the maximum acceptable skewangle. Similarly, when the skew angle returns to a value below themaximum acceptable skew angle, the antenna selection system 200 canswitch back to the primary antenna 152.

In the illustrated embodiment, range 494 of skew angles extends from theline 490 to the wide beamdwidth axis 450 (FIG. 4B) corresponding to theskew angle of ninety degrees. In such a case, the secondary antenna 154can avoid excessive interference with the non-target satellite 120 atall the geographic locations at which the main beam 480 of the secondaryantenna 154 has the contour illustrated in FIG. 4C. Alternatively, therange 494 of skew angles may not extend to the skew angle of 90 degrees.

The range 492 of skew angles and the range 494 of skew angles can varyfrom embodiment to embodiment. In some embodiments, range 492 of skewangles is at least 40 degrees, and the range 494 of skew angles is atleast 30 degrees. For example, range 492 of skew angles may be from zeroto sixty degrees, and range 494 of skew angles may be from sixty toninety degrees.

FIG. 5A illustrates an example acceptable service area 510 a, 510 b ofthe primary antenna 152. In the illustrated embodiment, the targetsatellite 110 and the non-target satellite 120 are both geostationarysatellites.

The acceptable service area 510 a, 510 b are geographic locations of theantenna system 150 where the amount of interference with the non-targetsatellite 120 when using the primary antenna 152 is at or below thethreshold, and the signal communication with the target satellite 110has acceptable or desired performance characteristics. In other words,within the acceptable service area 510 a, 510 b, the skew angle of mainbeam of the primary antenna 152 is less than the maximum acceptable skewangle. The boundary 512 corresponds to the line 490 of FIG. 4B. In theillustrated example, the acceptable service area 510 a, 510 b accountfor the attitude of the aircraft 102.

The maximum acceptable skew angle, and thus the acceptable service area510 a, 510 b of the primary antenna 152, can vary from embodiment toembodiment. The maximum acceptable skew angle can depend on theradiation pattern of the primary antenna 152, the locations of thetarget satellite 110 and non-target satellite 120, the threshold amountof interference with the non-target satellite 120, the transmissionparameters of the return uplink signal 116, etc.

As described above, the skew angle of the main beam 422 of the primaryantenna 512, and thus the composite half-power beamwidth along the geoarc, varies depending upon the geographic location of the antenna system150. FIG. 5B illustrates the contour of the main beam 422 of the primaryantenna 152 for an example geographic location 520 within the acceptableservice area 510 a, 510 b. In this example, the composite half-powerbeamwidth along the geo arc 540 is small enough that the amount ofinterference with the non-target satellite 120 is less than or equal tothe threshold.

FIG. 5C illustrates the contour of the main beam 422 of the primaryantenna 152 for an example geographic location 530 outside theacceptable service area 510 a, 510 b. In this example, the compositehalf-power beamwidth along the geo arc 540 is large enough to causeexcessive interference with the non-target satellite 120, if the primaryantenna 152 were used to communication with the target satellite 110.

FIG. 5D illustrates an example acceptable service area 510 c of thesecondary antenna 154. The acceptable service area 510 c are geographiclocations where the amount of interference with the non-target satellite120 when using the secondary antenna 154 is at or below the threshold,and signal communication with the target satellite 110 has acceptable ordesired performance characteristics. In the illustrated embodiment, theacceptable service area 510 c is for a secondary antenna 154 thatincludes a non-movable, fully electronic scanning phased array antenna.At higher latitudes around the same longitude as the target satellite110, the boundary 514 of the acceptable service area 510 c can be due toscan loss of the array which precludes signal communication havingacceptable performance characteristics with the target satellite 110. Atlower latitudes near the equator 500, the boundary 514 can be due to anincrease in the composite half-power beamwidth of the main beam 480along the geo arc at larger scan angles to the target satellite 110.

As can be seen upon comparison of FIGS. 5A and 5D, in the illustratedembodiment a portion of the acceptable service area 510 c of thesecondary antenna 514 overlaps with the acceptable service area 510 a,510 b of the primary antenna 512. The determination of whether to usethe primary antenna 512 or the secondary antenna 514 when the aircraft102 is at a geographic location within this overlap can vary fromembodiment to embodiment. For example, at a given geographic locationwith this overlap, the antenna selection system 200 can select theprimary antenna 152 or secondary antenna 154 based on which antenna 152,154 provides performance characteristics at the given geographiclocation for communicating with the target satellite 110. In embodimentsin which the primary antenna 152 can provide better performancecharacteristics than the secondary antenna 154 for communicating withthe target satellite 110 when the aircraft 102 is throughout theoverlap, the antenna selection system 200 can select the primary antenna152 for use.

FIG. 5E illustrates an example composite acceptable service area 510 dfor the antenna system 150. The composite acceptable service area 510 dare geographic locations where the amount of interference with thenon-target satellite 120, when using the primary antenna 152 or thesecondary antenna 154, is at or below the threshold, and signalcommunication with the target satellite 110 has acceptable or desiredperformance characteristics. The composite acceptable service area 510 dis a union of the acceptable service area 510 a, 510 b of the primaryantenna 512 and the acceptable service area 510 c of the secondaryantenna 514. As can be seen in FIG. 5E, the primary antenna 512 and thesecondary antenna 514 provides a larger acceptable service area than asystem that includes only one of the antennas 152, 154.

In the illustrated embodiment of FIG. 5E, the primary antenna 152 isselected by the antenna selection system 200 for use within the overlapbetween the acceptable service area 510 a, 510 b of the primary antenna152 and the acceptable service area 510 c of the secondary antenna 154.In some alternative embodiments, the antenna selection system 200 mayselect the secondary antenna 154 for use within some or all of theoverlap.

Line 550 represents an example flight path for the aircraft 102 betweensource 552 and destination 554. At geographic locations along a firstsegment 570 of the flight path, the aircraft 102 is within theacceptable service area 510 b of the primary antenna 152. Thus, alongthe first segment 570 the antenna selection system 200 selects theprimary antenna 152 for communication with the target satellite 110. Atgeographic location 556 the aircraft 102 leaves the acceptable servicearea 510 b of the primary antenna 152 and enters the acceptable servicearea 510 c of the secondary antenna 154. Thus, at geographic location556 the antenna selection system 200 switches communication with thetarget satellite 110 from the primary antenna 152 to the secondaryantenna 154, and continues to use the secondary antenna 154 along thesegment 572. At geographic location 558 the aircraft 102 enters theacceptable service area 510 a of the primary antenna 152. Thus, atgeographic location 558 the antenna selection system 200 switchescommunication with the target satellite 110 from the secondary antenna154 to the primary antenna 152, and continues to use the primary antenna152 along the segment 574 to the destination 554.

In the illustrated embodiment the antenna selection system 200 switchescommunication between the primary antenna 152 and the secondary antenna514 at the boundaries between the various acceptable service areas. Inother embodiments, the switching along the flight path may occur atgeographic locations different than these boundaries. For example, if atleast a portion of the segment 574 adjacent geographic location 558 iswithin the overlap of the acceptable service areas 510 a, 510 c, theantenna selection system 200 may continue to use the secondary antenna154 for some or all of that portion. In contrast, if the flight pathwere in the other direction, the antenna selection system 200 switchesfrom the primary antenna 152 to the secondary antenna 154 at geographiclocation 558, since a portion of the segment 572 adjacent the geographiclocation 558 is not within the overlap of the acceptable service areasof the primary antenna 152 and the secondary antenna 154. In otherwords, the geographic locations at which the antenna selection system200 switches between the primary antenna 152 and the secondary antenna154 may depend on whether the aircraft 102 is moving from the acceptableservice area 510 a, 510 b of the primary antenna 152 to the acceptableservice area 510 c of the secondary antenna 154, or is moving from theacceptable service area 510 c of the secondary antenna 154 to theacceptable service area 510 a, 510 b of the primary antenna 152.

FIG. 6 is an example graph of maximum power spectral density (PSD)curves for the primary antenna 512 and the secondary antenna 514 thatsatisfy interference requirements with the non-target satellite 120. Ascan be seen in the graph, the curve 600 of the maximum PSD for theprimary antenna 512 decreases with increasing skew angle. This is due tothe increase in the composite beamwidth of the main beam 422 of theprimary antenna 512 as the skew angle increases. In contrast, the curve610 of the maximum PSD for the secondary antenna 514 increases as theskew angle of the main beam 422 of the primary antenna 512 approaches 90degrees. This is due to the increasing projected aperture of thesecondary antenna 154 along the line defined by the target satellite 110and the non-target satellite 120. In other words, the compositehalf-power beamwidth of the secondary antenna decreases as the skewangle of the primary antenna increases.

In the illustrated embodiment of FIG. 6, the switching by the antennaselection system 200 between the primary antenna 152 and the secondaryantenna 154 occurs over a non-zero switching range 620 between skewangle S₁ and skew angle S2. The switching range 620 corresponds to atleast a portion of the overlap between the acceptable service areas ofthe primary antenna 152 and the secondary antenna 154. The switching bythe antenna selection system 200 from the primary antenna 152 to thesecondary antenna 154 occurs at skew angle S2, whereas the switchingfrom the secondary antenna 154 to the primary antenna 152 occurs at skewangle S₁. The skew angle S2 may for example correspond to geographiclocations (e.g. geographic location 556) along the boundary of theacceptable service area 510 a, 510 b of the primary antenna 152. Theskew angle S₁ can correspond to geographic locations within the overlapand inside the boundary of the acceptable service area 510 a, 510 b ofthe primary antenna 152. By having separate skew angle values S₁, S₂,rapid switching can be avoided when the aircraft 102 flies near theboundaries of the acceptable service area 510 a, 510 b of the primaryantenna 152 and the acceptable service area 510 c of the secondaryantenna 154. In alternative embodiments, the skew angle 51 and skewangle S2 may be the same.

As can be seen in FIG. 6, the minimum PSD P_(min) over the range of skewangles from 0 to 90 degrees that the antenna system 150 can provide byswitching between the primary antenna 152 and the secondary antenna 154is significantly greater than can be provided by either antenna 152, 154separately.

FIG. 7 is an example plot 700 of the maximum value of the gain of theprimary antenna 152 at 2 degrees from boresight of the main beam versusskew angle. Line 710 represents the maximum value of the gain thatsatisfies interference requirements with the non-target satellite 120.As can be seen in FIG. 7, the plot 700 crosses the line 710 at a skewangle value of about 65 degrees in this example. Thus, in this examplethe maximum acceptable skew angle for the primary antenna 152 is about65 degrees.

FIG. 8 illustrates an example process 800 for switching between theprimary antenna 512 and the secondary antenna 514. Other embodiments cancombine some of the steps, can perform the steps in different ordersand/or perform different or additional steps to the ones illustrated inFIG. 8. In the illustrated embodiment, the process 800 includes stepsperformed by the antenna selection system 200 discussed above.

At step 802, a signal is communicated between a target satellite and anaircraft via a primary antenna on the aircraft. In the illustratedembodiment, the primary antenna is mechanically steerable and has anasymmetric antenna beam pattern with a narrow beamwidth axis and a widebeamwidth axis at boresight. The primary antenna can for example be theprimary antenna 152 discussed above.

At step 804, the determination of whether an amount of interference witha non-target satellite reaches a threshold due to the wide beamwidthaxis of the asymmetric antenna beam pattern. If not, the process 500returns to step 802.

If the determination is made at step 804 that the amount of interferencewith the non-target satellite reaches the threshold, the processcontinues to step 806. At step 806, communication of the signal isswitched from the primary antenna to a secondary antenna on the aircraftto reduce interference. The secondary antenna can for example be thesecondary antenna 154 discussed above.

At step 808, the signal is communicated between the target satellite andthe aircraft via the secondary antenna.

At step 810, the determination of whether an amount of interference withthe non-target satellite using primary antenna will be below thethreshold. The step 810 can for example be performed as the aircraft 102moves. If not, the process returns to step 808.

If the determination is made at step 810 that the amount of interferencewith the non-target satellite using the primary antenna will be belowthe threshold, the process returns to step 802.

While the present disclosure is described by reference to the examplesdetailed above, it is to be understood that these examples are intendedin an illustrative rather than in a limiting sense. It is contemplatedthat modifications and combinations will readily occur to those skilledin the art, which modifications and combinations will be within thespirit of the disclosure and the scope of the following claims.

1. (canceled)
 2. An antenna system for mounting on an aircraft, theantenna system comprising: one or more first antenna elements configuredto form a first beam between the antenna system and one or moresatellites; one or more second antenna elements configured to form asecond beam between the antenna system and the one or more satellites;and an antenna selection system configured to: select the one or morefirst antenna elements to perform communications between the antennasystem and the one or more satellites via the first beam; switch a firstportion of the communications from the first beam formed by the one ormore first antenna elements to the second beam formed by the one or moresecond antenna elements when a performance characteristic associatedwith the first beam satisfies a threshold; and maintain a second portionof the communications via the first beam upon switching the firstportion of the communications to the second beam.
 3. The antenna systemof claim 2, wherein the antenna selection system is further configuredto: switch the first portion of the communications from the first beamto the second beam based at least in part on a geographic location ofthe antenna system, a flight path associated with the antenna system, orboth.
 4. The antenna system of claim 2, wherein the first portion of thecommunications comprises an uplink portion of the communications and thesecond portion of the communications comprises a downlink portion of thecommunications.
 5. The antenna system of claim 2, wherein theperformance characteristic associated with the first beam comprises anamount of interference with a non-target satellite.
 6. The antennasystem of claim 2, further comprising: a transceiver configured totransmit signals to the one or more satellites via the one or more firstantenna elements or the one or more second antenna elements and receivesignals from the one or more satellites via the one or more firstantenna elements or the one or more second antenna elements.
 7. Theantenna system of claim 6, further comprising: a modem coupled with thetransceiver and configured to: modulate uplink data to obtain modulateduplink data; transmit the modulated uplink data to the transceiver; andreceive modulated downlink data from the transceiver.
 8. The antennasystem of claim 2, further comprising: a transceiver configured totransmit uplink signals to the one or more satellites via the one ormore second antenna elements and receive signals from the one or moresatellites via the one or more first antenna elements based at least inpart on the antenna selection system switching the first portion of thecommunications to the second beam.
 9. A method for communications,comprising: forming, between an antenna system and one or moresatellites, a first beam using one or more first antenna elements and asecond beam using one or more second antenna elements; performingcommunications between the antenna system and the one or more satellitesvia the first beam; switching a first portion of the communications fromthe first beam to the second beam when a performance characteristicassociated with the first beam satisfies a threshold; and maintaining asecond portion of the communications via the first beam upon switchingthe first portion of the communications to the second beam.
 10. Themethod of claim 9, wherein the first portion of the communications isswitched from the first beam to the second beam based at least in parton a geographic location of the antenna system, a flight path associatedwith the antenna system, or both.
 11. The method of claim 9, wherein thefirst portion of the communications comprises an uplink portion of thecommunications and the second portion of the communications comprises adownlink portion of the communications.
 12. The method of claim 9,wherein the performance characteristic associated with the first beamcomprises an amount of interference with a non-target satellite.
 13. Themethod of claim 9, further comprising: transmitting, by a transceiver,signals to the one or more satellites via the one or more first antennaelements or the one or more second antenna elements and receive signalsfrom the one or more satellites via the one or more first antennaelements or the one or more second antenna elements.
 14. The method ofclaim 13, further comprising: modulating uplink data to obtain modulateduplink data; transmitting the modulated uplink data to the transceiver;and receiving modulated downlink data from the transceiver.
 15. Themethod of claim 9, further comprising: transmitting, by a transceiver,uplink signals to the one or more satellites via the one or more secondantenna elements; and receiving, by the transceiver, signals from theone or more satellites via the one or more first antenna elements basedat least in part on switching the first portion of the communications tothe second beam.